Polyolefin film and production thereof

Abstract

Biaxially oriented films and processes of forming such are generally described herein. The biaxially oriented film generally includes a polyolefin polymer and a moisture inhibiting agent to increase the opacity of the film.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/662,334, filed Mar. 16, 2005.

FIELD

Embodiments of the present invention generally relate to biaxially oriented films and production thereof.

BACKGROUND

Biaxially oriented films are used in a variety of applications as a result of the strength, clarity and barrier properties of the films. However, some applications, such as packaging and labeling, require increased porosity and/or opacity.

Therefore, a need exists to develop a biaxially oriented film that retains the strength of traditional films, while improving the porosity and opacity of the films.

SUMMARY

Embodiments of the present invention include a biaxially oriented film. The biaxially oriented film generally includes a polyolefin polymer and a moisture inhibiting agent.

Embodiments further include a method of forming a biaxially oriented film. The method generally includes providing a polyolefin polymer, incorporating additives, such as a moisture inhibiting additive and a cavitating agent, the cavitating agent including polybutylene terphthalate, into the polyolefin polymer and forming the polyolefin polymer including the additives into a biaxially oriented film.

Embodiments further include polymer articles formed from the films described herein.

DETAILED DESCRIPTION

Introduction and Definitions

A detailed description will now be provided. Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims. Each of the inventions will now be described in greater detail below, including specific embodiments, versions and examples, but the inventions are not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the inventions when the information in this patent is combined with available information and technology.

Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents. Further, unless otherwise specified, all compounds described herein may be substituted or unsubstituted and the listing of compounds includes derivatives thereof.

Embodiments of the present invention include biaxially oriented films and processes of forming such films. The films generally include a polyolefin polymer.

Certain polymerization processes disclosed herein involve contacting polyolefin monomers with one or more catalyst systems to form a polymer.

Catalyst Systems

The catalyst systems used herein may be characterized as supported catalyst systems or as unsupported catalyst systems, sometimes referred to as homogeneous catalysts. The catalyst systems may be metallocene catalyst systems, Ziegler-Natta catalyst systems or other catalyst systems known to one skilled in the art for the production of polyolefins, for example. A brief discussion of such catalyst systems is included below, but is in no way intended to limit the scope of the invention to such catalysts.

A. Ziegler-Natta Catalyst System

Ziegler-Natta catalyst systems are generally formed from the combination of a metal component (e.g., a catalyst precursor) with one or more additional components, such as a catalyst support, a cocatalyst and/or one or more electron donors.

A specific example of a catalyst precursor is a metal component generally represented by the formula:
MR_x;
where M is a transition metal, R is a halogen, an alkoxy, or a hydrocarboxyl group and x is the valence of the transition metal. For example, x may be from 1 to 4. The transition metal of the Ziegler-Natta catalyst compound, as described throughout the specification and claims, may be selected from Groups IV through VIB in one embodiment and selected from titanium, chromium, or vanadium in a more particular embodiment. R may be selected from chlorine, bromine, carbonate, ester, or an alkoxy group in one embodiment. Examples of catalyst precursors include TiCl₄, TiBr₄, Ti(OC₂H₅)₃Cl, Ti(OC₃H₇)₂Cl₂, Ti(OC₆H₁₃)₂Cl₂, Ti(OC₂H₅)₂Br₂ and Ti(OC₁₂H₂₅)Cl₃.

Those skilled in the art will recognize that a catalyst is “activated” in some way before it is useful for promoting polymerization. As discussed further below, activation may be accomplished by combining the catalyst with an activator, which is also referred to in some instances as a “cocatalyst.” As used herein, the term “Z-N activator” refers to any compound or combination of compounds, supported or unsupported, which may activate a Z-N catalyst precursor. Embodiments of such activators include organoaluminum compounds, such as trimethyl aluminum (TMA), triethyl aluminum (TEAl) and triisobutyl aluminum (TiBAl), for example.

The Ziegler-Natta catalyst system may further include one or more electron donors, such as internal electron donors and/or external electron donors. Internal electron donors may be used to reduce the atactic form of the resulting polymer, thus decreasing the amount of xylene solubles in the polymer. A polymer is “atactic” when its pendant groups are arranged in a random fashion on both sides of the chain of the polymer. In contrast, a polymer is “isotactic” when all of its pendant groups are arranged on the same side of the chain and “syndiotactic” when its pendant groups alternate on opposite sides of the chain. The internal electron donors may include amines, amides, esters, ketones, nitriles, ethers and phosphines in one embodiment. The internal electron donors include diethers, succinates and thalates, such as those described in U.S. Pat. No. 5,945,366, which is incorporated by reference herein, in a more particular embodiment. The internal electron donors include dialkoxybenzenes, such as those described in U.S. Pat. No. 6,399,837, which is incorporated by reference herein, in another embodiment.

External electron donors may be used to further control the amount of atactic polymer produced. The external electron donors may include monofunctional or polyfunctional carboxylic acids, carboxylic anhydrides, carboxylic esters, ketones, ethers, alcohols, lactones, organophosphorus compounds and/or organosilicon compounds. In one embodiment, the external donor may include diphenyldimethoxysilane (DPMS), cyclohexymethyldimethoxysilane (CDMS), diisopropyldimethoxysilane and/or dicyclopentyldimethoxysilane (CPDS). The external donor may be the same or different from the internal electron donor used.

The components of the Ziegler-Natta catalyst system (e.g., catalyst precursor, activator and/or electron donors) may or may not be associated with a support, either in combination with each other or separate from one another. Typical support materials may include a magnesium dihalide, such as magnesium dichloride or magnesium dibromide, for example.

Ziegler-Natta catalyst systems and processes for forming such catalyst systems are described in at least U.S. Pat. No. 4,298,718, U.S. Pat. No. 4,544,717 and U.S. Pat. No. 4,767,735, which are incorporated by reference herein.

B. Metallocene Catalyst System

Metallocene catalysts may be characterized generally as coordination compounds incorporating one or more cyclopentadienyl (Cp) groups (which may be substituted or unsubstituted, each substitution being the same or different) coordinated with a transition metal through π bonding.

The Cp substituent groups may be linear, branched or cyclic hydrocarbyl radicals. The cyclic hydrocarbyl radicals may further form other contiguous ring structures, including, for example indenyl, azulenyl and fluorenyl groups. These additional ring structures may also be substituted or unsubstituted by hydrocarbyl radicals, such as C₁ to C₂₀ hydrocarbyl radicals.

A specific example of a metallocene catalyst is a bulky ligand metallocene compound generally represented by the formula:
[L]_mM[A]_n;
where L is a bulky ligand, A is a leaving group, M is a transition metal and m and n are such that the total ligand valency corresponds to the transition metal valency. For example m may be from 1 to 3 and n may be from 1 to 3.

The metal atom “M” of the metallocene catalyst compound, as described throughout the specification and claims, may be selected from Groups 3 through 12 atoms and lanthanide Group atoms in one embodiment, selected from Groups 3 through 10 atoms in a more particular embodiment, selected from Sc, Ti, Zr, Hf, V, Nb, Ta, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, and Ni in yet a more particular embodiment, selected from Groups 4, 5 and 6 atoms in yet a more particular embodiment, Ti, Zr, Hf atoms in yet a more particular embodiment and Zr in yet a more particular embodiment. The oxidation state of the metal atom “M” may range from 0 to +7 in one embodiment, in a more particular embodiment, is +1, +2, +3, +4 or +5 and in yet a more particular embodiment is +2, +3 or +4. The groups bound the metal atom “M” are such that the compounds described below in the formulas and structures are electrically neutral, unless otherwise indicated.

The bulky ligand generally includes a cyclopentadienyl group (Cp) or a derivative thereof. The Cp ligand(s) form at least one chemical bond with the metal atom M to form the “metallocene catalyst compound”. The Cp ligands are distinct from the leaving groups bound to the catalyst compound in that they are not highly susceptible to substitution/abstraction reactions.

Cp typically includes fused ring(s) or ring systems. The ring(s) or ring system(s) typically include atoms selected from group 13 to 16 atoms, for example, carbon, nitrogen, oxygen, silicon, sulfur, phosphorous, germanium, boron, aluminum and combinations thereof, wherein carbon makes up at least 50% of the ring members. Non-limiting examples include cyclopentadienyl, cyclopentaphenanthreneyl, indenyl, benzindenyl, fluorenyl, tetrahydroindenyl, octahydrofluorenyl, cyclooctatetraenyl, cyclopentacyclododecene, phenanthrindenyl, 3,4-benzofluorenyl, 9-phenylfluorenyl, 8-H-cyclopent[a]acenaphthylenyl, 7-H-dibenzofluorenyl, indeno[1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl, hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl or H₄Ind), substituted versions thereof and heterocyclic versions thereof.

Cp substituent groups may include hydrogen radicals, alkyls, alkenyls, alkynyls, cycloalkyls, aryls, acyls, aroyls, alkoxys, aryloxys, alkylthiols, dialkylamines, alkylamidos, alkoxycarbonyls, aryloxycarbonyls, carbomoyls, alkyl- and dialkyl-carbamoyls, acyloxys, acylaminos, aroylaminos and combinations thereof. More particular non-limiting examples of alkyl substituents include methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, benzyl, phenyl, methylphenyl, and tert-butylphenyl groups and the like, including all their isomers, for example tertiary-butyl, isopropyl and the like. Other possible radicals include substituted alkyls and aryls such as, for example, fluoromethyl, fluroethyl, difluroethyl, iodopropyl, bromohexyl, chlorobenzyl and hydrocarbyl substituted organometalloid radicals including trimethylsilyl, trimethylgermyl, methyldiethylsilyl and the like, halocarbyl-substituted organometalloid radicals including tris(trifluoromethyl)silyl, methylbis(difluoromethyl)silyl, bromomethyldimethylgermyl and the like, disubstituted boron radicals including dimethylboron for example, disubstituted Group 15 radicals including dimethylamine, dimethylphosphine, diphenylamine, methylphenylphosphine and Group 16 radicals including methoxy, ethoxy, propoxy, phenoxy, methylsulfide and ethylsulfide. Other substituents R include olefins, such as but not limited to, olefinically unsaturated substituents including vinyl-terminated ligands, for example 3-butenyl, 2-propenyl, 5-hexenyl and the like. In one embodiment, at least two R groups, two adjacent R groups in one embodiment, are joined to form a ring structure having from 3 to 30 atoms selected from carbon, nitrogen, oxygen, phosphorous, silicon, germanium, aluminum, boron and combinations thereof. Also, a substituent group R group such as 1-butanyl, may form a bonding association to the element M.

Each anionic leaving group is independently selected and may include any leaving group, such as halogen ions, hydrides, C₁ to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀ alkylaryls, C₁ to C₁₂ alkoxys, C₆ to C₁₆ aryloxys, C₇ to C₁₈ alkylaryloxys, C₁ to C₁₂ fluoroalkyls, C₆ to C₁₂ fluoroaryls, C₁ to C₁₂ heteroatom-containing hydrocarbons and substituted derivatives thereof, hydride, halogen ions, C₁ to C₆ alkylcarboxylates, C₁ to C₆ fluorinated alkylcarboxylates, C₆ to C₁₂ arylcarboxylates, C₇ to C₁₈ alkylarylcarboxylates, C₁ to C₆ fluoroalkyls, C₂ to C₆ fluoroalkenyls and C₇ to C₁₈ fluoroalkylaryls in yet a more particular embodiment, hydride, chloride, fluoride, methyl, phenyl, phenoxy, benzoxy, tosyl, fluoromethyls and fluorophenyls in yet a more particular embodiment, C₁ to C₁₂ alkyls, C₂ to C₁₂ alkenyls, C₆ to C₁₂ aryls, C₇ to C₂₀ alkylaryls, substituted C₁ to C₁₂ alkyls, substituted C₆ to C₁₂ aryls, substituted C₇ to C₂₀ alkylaryls, C₁ to C₁₂ heteroatom-containing alkyls, C₁ to C₁₂ heteroatom-containing aryls and C₁ to C₁₂ heteroatom-containing alkylaryls in yet a more particular embodiment, chloride, fluoride, C₁ to C₆ alkyls, C₂ to C₆ alkenyls, C₇ to C₁₈ alkylaryls, halogenated C₁ to C₆ alkyls, halogenated C₂ to C₆ alkenyls and halogenated C₇ to C₁₈ alkylaryls in yet a more particular embodiment, fluoride, methyl, ethyl, propyl, phenyl, methylphenyl, dimethylphenyl, trimethylphenyl, fluoromethyls (mono-, di- and trifluoromethyls) and fluorophenyls (mono-, di-, tri-, tetra- and pentafluorophenyls) in yet a more particular embodiment and fluoride in yet a more particular embodiment.

Other non-limiting examples of leaving groups include amines, phosphines, ethers, carboxylates, dienes, hydrocarbon radicals having from 1 to 20 carbon atoms, fluorinated hydrocarbon radicals (e.g., —C₆F₅ (pentafluorophenyl)), fluorinated alkylcarboxylates (e.g., CF₃C(O)O⁻), hydrides, halogen ions and combinations thereof. Other examples of leaving groups include alkyl groups such as cyclobutyl, cyclohexyl, methyl, heptyl, tolyl, trifluoromethyl, tetramethylene, pentamethylene, methylidene, methyoxy, ethyoxy, propoxy, phenoxy, bis(N-methylanilide), dimethylamide, dimethylphosphide radicals and the like. In one embodiment, two or more leaving groups form a part of a fused ring or ring system.

L and A may be bridged to one another. A bridged metallocene, for example may, be described by the general formula:
XCp^ACp^BMA_n;
wherein X is a structural bridge, Cp^A and Cp^B each denote a cyclopentadienyl group, each being the same or different and which may be either substituted or unsubstituted, M is a transition metal and A is an alkyl, hydrocarbyl or halogen group and n is an integer between 0 and 4, and either 1 or 2 in a particular embodiment.

Non-limiting examples of bridging groups (X) include divalent hydrocarbon groups containing at least one Group 13 to 16 atom, such as but not limited to, at least one of a carbon, oxygen, nitrogen, silicon, aluminum, boron, germanium, tin and combinations thereof; wherein the heteroatom may also be C₁ to C₁₂ alkyl or aryl substituted to satisfy neutral valency. The bridging group may also contain substituent groups as defined above including halogen radicals and iron. More particular non-limiting examples of bridging groups are represented by C₁ to C₆ alkylenes, substituted C₁ to C₆ alkylenes, oxygen, sulfur, R₂C═, R₂Si═, —Si(R)₂Si(R₂)—and R₂Ge═, RP═ (wherein “═” represents two chemical bonds), where R is independently selected from the group hydride, hydrocarbyl, substituted hydrocarbyl, halocarbyl, substituted halocarbyl, hydrocarbyl-substituted organometalloid, halocarbyl-substituted organometalloid, disubstituted boron, disubstituted Group 15 atoms, substituted Group 16 atoms and halogen radicals and wherein two or more Rs may be joined to form a ring or ring system. In one embodiment, the bridged metallocene catalyst component has two or more bridging groups (X).

As used herein, the term “metallocene activator” is defined to be any compound or combination of compounds, supported or unsupported, which may activate a single-site catalyst compound (e.g., metallocenes, Group 15 containing catalysts, etc.) Typically, this involves the abstraction of at least one leaving group (A group in the formulas/structures above, for example) from the metal center of the catalyst component. The catalyst components of the present invention are thus activated towards olefin polymerization using such activators. Embodiments of such activators include Lewis acids such as cyclic or oligomeric polyhydrocarbylaluminum oxides and so called non-coordinating ionic activators (“NCA”), alternately, “ionizing activators” or “stoichiometric activators”, or any other compound that may convert a neutral metallocene catalyst component to a metallocene cation that is active with respect to olefin polymerization.

More particularly, it is within the scope of this invention to use Lewis acids such as alumoxane (e.g., “MAO”), modified alumoxane (e.g., “TIBAO”) and alkylaluminum compounds as activators, to activate desirable metallocenes described herein. MAO and other aluminum-based activators are well known in the art. Non-limiting examples of aluminum alkyl compounds which may be utilized as activators for the catalysts described herein include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum and the like.

Ionizing activators are well known in the art and are described by, for example, Eugene You-Xian Chen & Tobin J Marks, Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure-Activity Relationships 100(4) CHEMICAL REVIEWS 1391-1434 (2000). Examples of neutral ionizing activators include Group 13 tri-substituted compounds, in particular, tri-substituted boron, tellurium, aluminum, gallium and indium compounds and mixtures thereof (e.g., tri(n-butyl)ammonium tetrakis(pentafluorophenyl)boron and/or trisperfluorophenyl boron metalloid precursors). The three substituent groups are each independently selected from alkyls, alkenyls, halogen, substituted alkyls, aryls, arylhalides, alkoxy and halides. In one embodiment, the three groups are independently selected from the group of halogen, mono or multicyclic (including halosubstituted) aryls, alkyls, alkenyl compounds and mixtures thereof. In another embodiment, the three groups are selected from the group alkenyl groups having 1 to 20 carbon atoms, alkyl groups having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, aryl groups having 3 to 20 carbon atoms (including substituted aryls) and combinations thereof. In yet another embodiment, the three groups are selected from the group alkyls having 1 to 4 carbon groups, phenyl, naphthyl and mixtures thereof. In yet another embodiment, the three groups are selected from the group highly halogenated alkyls having 1 to 4 carbon groups, highly halogenated phenyls, highly halogenated naphthyls and mixtures thereof. By “highly halogenated”, it is meant that at least 50% of the hydrogens are replaced by a halogen group selected from fluorine, chlorine and bromine. In yet another embodiment, the neutral stoichiometric activator is a tri-substituted Group 13 compound comprising highly fluorided aryl groups, the groups being highly fluorided phenyl and highly fluorided naphthyl groups.

The activators may or may not be associated with or bound to a support, either in association with the catalyst component (e.g., metallocene) or separate from the catalyst component, such as described by Gregory G. Hlatky, Heterogeneous Single-Site Catalysts for Olefin Polymerization 100(4) CHEMICAL REVIEWS 1347-1374 (2000).

Metallocene Catalysts may be supported or unsupported. Typical support materials may include talc, inorganic oxides, clays and clay minerals, ion-exchanged layered compounds, diatomaceous earth compounds, zeolites or a resinous support material, such as a polyolefin.

Specific inorganic oxides include silica, alumina, magnesia, titania and zirconia, for example. The inorganic oxides used as support materials may have an average particle size of from 30 microns to 600 microns or from 30 microns to 100 microns, a surface area of from 50 m²/g to 1,000 m²/g or from 100 m²/g to 400 m²/g and a pore volume of from 0.5 cc/g to 3.5 cc/g or from 0.5 cc/g to 2 cc/g. Desirable methods for supporting metallocene ionic catalysts are described in U.S. Pat. No. 5,643,847; 09184358 and 09184389, which are incorporated by reference herein.

Polymerization Processes

As indicated elsewhere herein, catalyst systems are used to make polyolefin compositions. Once the catalyst system is prepared, as described above and/or as known to one skilled in the art, a variety of processes can be carried out using that composition. Among the varying approaches that can be used include procedures set forth in U.S. Pat. No. 5,525,678, incorporated by reference herein. The equipment, process conditions, reactants, additives and other materials will of course vary in a given process, depending on the desired composition and properties of the polymer being formed. For example, the processes of U.S. Pat. No. 6,420,580, U.S. Pat. No. 6,380,328, U.S. Pat. No. 6,359,072, U.S. Pat. No. 6,346,586, U.S. Pat. No. 6,340,730, U.S. Pat. No. 6,339,134, U.S. Pat. No. 6,300,436, U.S. Pat. No. 6,274,684, U.S. Pat. No. 6,271,323, U.S. Pat. No. 6,248,845, U.S. Pat. No. 6,245,868, U.S. Pat. No. 6,245,705, U.S. Pat. No. 6,242,545, U.S. Pat. No. 6,211,105, U.S. Pat. No. 6,207,606, U.S. Pat. No. 6,180,735 and U.S. Pat. No. 6,147,173 may be used and are incorporated by reference herein.

The catalyst systems described above can be used in a variety of polymerization processes, over a wide range of temperatures and pressures. The temperatures may be in the range of from about −60° C. to about 280° C., or from about 50° C. to about 200° C. and the pressures employed may be in the range of from 1 atmosphere to about 500 atmospheres or higher.

Polymerization processes may include solution, gas phase, slurry phase, high pressure processes or a combination thereof.

In certain embodiments, the process of the invention is directed toward a solution, high pressure, slurry or gas phase polymerization process of one or more olefin monomers having from 2 to 30 carbon atoms, or from 2 to 12 carbon atoms or from 2 to 8 carbon atoms, such as ethylene, propylene, butane, pentene, methylpentene, hexane, octane and decane. Other monomers include ethylenically unsaturated monomers, diolefins having from 4 to 18 carbon atoms, conjugated or nonconjugated dienes, polyenes, vinyl monomers and cyclic olefins. Non-limiting monomers may include norbornene, nobornadiene, isobutylene, isoprene, vinylbenzocyclobutane, sytrnes, alkyl substituted styrene, ethylidene norbornene, dicyclopentadiene, and cyclopentene. In one embodiment, a copolymer is produced, such as propylene/ethylene, or a terpolymer is produced. Examples of solution processes are described in U.S. Pat. No. 4,271,060, U.S. Pat. No. 5,001,205, U.S. Pat. No. 5,236,998 and U.S. Pat. No. 5,589,555, which are incorporated by reference herein.

One example of a gas phase polymerization process generally employs a continuous cycle, wherein a cycling gas stream (otherwise known as a recycle stream or fluidizing medium) is heated in a reactor by heat of polymerization. The heat is removed from the recycle stream in another part of the cycle by a cooling system external to the reactor. The gaseous stream containing one or more monomers may be continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and fresh monomer is added to replace the polymerized monomer. (See, for example, U.S. Pat. No. 4,543,399, U.S. Pat. No. 4,588,790, U.S. Pat. No. 5,028,670, U.S. Pat. No. 5,317,036, U.S. Pat. No. 5,352,749, U.S. Pat. No. 5,405,922, U.S. Pat. No. 5,436,304, U.S. Pat. No. 5,456,471, U.S. Pat. No. 5,462,999, U.S. Pat. No. 5,616,661 and U.S. Pat. No. 5,668,228, which are incorporated by reference herein.)

The reactor pressure in a gas phase process may vary from about 100 psig to about 500 psig, or from about 200 psig to about 400 psig or from about 250 psig to about 350 psig, for example. The reactor temperature in a gas phase process may vary from about 30° C. to about 120° C., or from about 60° C. to about 115° C., or from about 70° C. to about 110° C. or from about 70° C. to about 95° C. Other gas phase processes contemplated by the process includes those described in U.S. Pat. No. 5,627,242, U.S. Pat. No. 5,665,818 and U.S. Pat. No. 5,677,375, which are incorporated by reference herein.

Slurry processes generally include forming a suspension of solid, particulate polymer in a liquid polymerization medium, to which monomers and optionally hydrogen, along with catalyst, are added. The suspension (which may include diluents) can be intermittently or continuously removed from the reactor where the volatile components can be separated from the polymer and recycled, optionally after a distillation, to the reactor. The liquefied diluent employed in the polymerization medium is typically an alkane having from 3 to 7 carbon atoms, such as a branched alkane. The medium employed is generally liquid under the conditions of polymerization and relatively inert. Such as hexane or isobutene.

In a specific embodiment, a slurry process or a bulk process (e.g., a process without a diluent) may be carried out continuously in one or more loop reactors. The catalyst, as a slurry or as a dry free flowing powder, can be injected regularly to the reactor loop, which can itself be filled with circulating slurry of growing polymer particles in a diluent. Hydrogen, optionally, may be added as a molecular weight control. The reactor may be maintained at a pressure of from about 27 bar to about 45 bar and a temperature of from about 38° C. to about 121° C., for example. Reaction heat can be removed through the loop wall since much of the reactor is in the form of a double-jacketed pipe. The slurry may exit the reactor at regular intervals or continuously to a heated low pressure flash vessel, rotary dryer and a nitrogen purge column in sequence form removal of the diluent and all unreacted monomer and comonomers. The resulting hydrocarbon free powder can then be compounded for use in various applications. Alternatively, other types of slurry polymerization processes can be used, such stirred reactors is series, parallel or combinations thereof.

Polymer Product

The polymers produced by the processes described herein can be used in a wide variety of products and end-use applications. The polymers include linear low density polyethylene, elastomers, plastomers, high density polyethylenes, low density polyethylenes, medium density polyethylenes, polypropylene and polypropylene copolymers.

In certain embodiments, propylene based polymers can be produced using the processes described herein. These polymers include atactic polypropylene, isotactic polypropylene, hemi-isotactic and syndiotactic polypropylene. Other propylene polymers include propylene block or impact copolymers.

Such propylene polymers may have a molecular weight distribution, i.e., a weight average molecular weight to number average molecular weight (Mw/Mn), of from about 2 to about 20, or from about 2 to about 12, for example, measured by gel permeation chromatography.

In addition, the propylene polymers may have a melt flow rate (MFR) measured by ASTM-D-1238-E of from about 0.01 dg/min to about 1000 dg/min. or from about 0.01 dg/min. to about 100 dg/min., or from about 0.02 dg/min. to about 50 dg/min. or from about 0.03 dg/min. to about 10 dg/min, for example.

The propylene polymers may further have a melting point of at least about 115° C., or from about 150° C. to about 167° C., for example, measured by DCS.

In one embodiment, the propylene polymer has a crystallinity measured by ¹³C NMR spectroscopy using meso pentads of from about 89% to about 99%.

Product Application

The polymers produced are useful in a variety of end-use applications, such as film production.

In one embodiment, the polymer is used to form a biaxially oriented film. Orientation of a polymer is the process whereby the directionality (the orientation of molecules relative to each other) is imposed upon the polymeric arrangements in the film. Such orientation is employed to impart desirable properties to films, such as toughness and opaqueness, for example. As used herein, the term “biaxial orientation” refers to a process in which the polymer is heated and extruded into a film, such film then being stressed in both a longitudinal direction (e.g., the machine direction) and in a transverse or lateral direction (e.g., the tenter direction).

Biaxial film production generally includes heating the polymer to a temperature at or above its glass-transition temperature but below its crystalline melting point, and then quickly stretching such polymer to form a film. On cooling, the molecular alignment imposed by stretching competes favorably with crystallization, and the drawn polymer molecules condense into a crystalline network with crystalline domains aligned in the direction of the drawing force.

In particular, a specific, non-limiting example includes passing a molten polymer over a first roller (e.g., a chill roller), solidifying the polymer into a film. The film is then oriented by stressing such film in a longitudinal direction and in a transverse direction. Alternatively, the film may be stressed in both directions at same time.

The longitudinal orientation is generally accomplished through the use of two sequentially disposed rollers, the second (or fast roller) operating at a speed in relation to the slower roller corresponding to the desired orientation ratio. Longitudinal orientation may alternatively be accomplished through a series of rollers with increasing speeds, sometimes with additional intermediate rollers for temperature control and other functions.

After longitudinal orientation, the film may be cooled, pre-heated and passed into a lateral orientation section. The lateral orientation section may include, for example, a tenter frame mechanism, where the film is stressed in the transverse direction.

Annealing and/or additional processing may follow such orientation.

Further, the process may include coextruding additional layers to form a multilayer film. The additional layers may be any coextrudable film known in the art, such as syndiotactic polypropylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-propylene copolymers, butylenes-propylene compolymers, ethylene-butylene copolymers, ethylene-propylene-butylene terpolymers, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, nylons etc.

In order to modify or enhance certain properties of the films for specific end-uses, it is possible for one or more of the layers to contain appropriate additives in effective amounts. The additives may be employed either in the application phase (formation of biaxial film) or may be combined with the polymer during the processing phase (pellet extrusion), for example. Such additives may include stabilizers (e.g., hindered amines, benzofuranon, indolinone) to protect against UV degradation, thermal or oxidative degradation and/or actinic degradation, antistatic agents (e.g., medium to high molecular weight polyhydric alcohols and tertiary amines), anti-blocks, coefficient of friction modifiers, processing aids, colorants, clarifiers and other additives known to those skilled in the art.

Examples of biaxial film production are included in at least U.S. Pat. No. 4,029,876 and U.S. Pat. No. 2,178,104, which are incorporated by reference herein.

In one embodiment, the polymer based films are formed for use in packaging (e.g., cups, trays, bottles, tubular containers and closures) and labeling, for example. Such films generally exhibit resistance to the transmission of moisture, air and deleterious flavors therethrough and further exhibit desirable mechanical properties, such as strength and clarity.

In one embodiment, the biaxial film is opaque. Opaque films generally have a void content (e.g., porosity) measured by density of at least 0.4, or from about 0.45 to about 1.5 or of at least 0.5, for example.

When forming opaque biaxial films, the process generally includes combining at least one cavitating agent with the polymer prior to extrusion and orientation. Such cavitating agent is generally capable of generating voids in the structure of the film during the film-making process. When a polymer including the cavitating agent is subjected to biaxial orientation, a cavity forms around the distributed dispersed phase moieties, providing a film having an opaque appearance. Such cavitating agent may include a polymer such as a polyester (e.g., polybutylene terephthalate (PBT)), nylon, an acrylic resin, polystyrene or an inorganic material (e.g., glass, metal or ceramic), for example. In one embodiment, the cavitating agent is present in an amount of up to about 1 wt. % to about 30 wt. %, or from about 3 wt. % to about 15 wt. % or from about 3 wt. % to about 12 wt. %.

PBT is a semicrystalline polymer having a low viscosity. Unfortunately, when PBT is used as the cavitating agent, the PBT may degrade, resulting in build up in the film production equipment. Such buildup may form deposits, which further affect the flow patterns of the molten polymer in the die (e.g., the equipment).

Further, specific packaging applications and labeling applications require higher porosity and opacity levels than typical polymer based films provide.

Embodiments of the invention contemplate combining a moisture-inhibiting agent with the polypropylene polymer prior to film formation. Such agent may be combined with the polymer at the same time as the cavitating agent, during polymer formation, such as prior to extrusion into pellets or at any other time for additive addition known to one skilled in the art.

The additive may be any which meets the objects of the embodiments described herein. Useful inhibitors include, but are not limited to, alumina (e.g., Al₂O₃), phosphorous pentoxide, siloxanes (e.g., hexamethyldisiloxane and tetramethyldisiloxane), silica, zeolite, phosphorous pentoxide and boron oxide, for example. It is contemplated that if the moisture inhibiting additive is the same compound as an additive included in the film for another purpose, such as the use of silica gel for an antiblocking agent, the moisture inhibiting additive will be included in an amount that is in addition to the amount used for another purpose. Further, the moisture inhibiting additive is added to the polymer prior to film formation.

It is anticipated that addition of such inhibitor will increase the porosity and opacity of propylene based biaxial films.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof and the scope thereof is determined by the claims that follow.

Claims

1. A biaxially oriented film comprising:

a polyolefin polymer; and

a moisture inhibiting agent.

2. The film of claim 1, wherein the polyolefin polymer comprises polypropylene.

3. The film of claim 2, wherein the polypropylene has a molecular weight distribution of from about 2 to about 12.

4. The film of claim 2, wherein the polypropylene has a melt flow rate of from about 0.03 dg/min. to about 10 dg/min.

5. The film of claim 2, wherein the polypropylene has a melting point of from about 150° C. to about 167° C.

6. The film of claim 2, wherein the polypropylene has a crystallinity of from about 89% to about 99%.

7. The film of claim 1, wherein the moisture inhibiting agent is selected from alumina, phosphorous, pentoxides, siloxanes, silicas, zeolites, oxides and combinations thereof.

8. The film of claim 1, wherein the film is opaque.

9. The film of claim 1 further comprising a cavitating agent.

10. The film of claim 9, wherein the film comprises from about 3 wt. % to about 15 wt. % cavitating agent.

11. The film of claim 9, wherein the cavitating agent is polybutylene terphthalate.

12. The film of claim 8, wherein the film has a density of from about 0.45 to about 1.5 g/cm3.

13. A method of forming a biaxially oriented film comprising:

providing a polyolefin polymer;

incorporating additives comprising a moisture inhibiting additive and a cavitating agent comprising polybutylene terphthalate into the polyolefin polymer; and

forming the polyolefin polymer including the additives into a biaxially oriented film.

14. The method of claim 13, wherein the moisture inhibiting agent is selected from alumina, phosphorous, pentoxides, siloxanes, silicas, zeolites, oxides and combinations thereof.

15. The method of claim 13, wherein the polyolefin polymer comprises polypropylene.

16. The method of claim 15, wherein the polypropylene has a crystallinity of from about 89% to about 99%.

17. The method of claim 13 further comprising forming the biaxially oriented film into a polymer article, wherein the polymer article requires opacity.

18. The method of claim 17, wherein the polymer article is selected from labels and packaging materials.

19. A polymer article comprising:

a biaxially oriented film comprising a polyolefin polymer, a moisture inhibiting additive and polybutylene terphthalate.

20. The polymer article of claim 19, wherein the polymer article is a label.

21. The polymer article of claim 19, wherein the polymer article is a packaging material.

22. The polymer article of claim 19, wherein the moisture inhibiting agent is selected from alumina, phosphorous, pentoxides, siloxanes, silicas, zeolites, oxides and combinations thereof.